bug #31779: Add support for addressing usbtinyisp with -P option
* usbtiny.c (usbtiny_open): Add logic to distinguish multiple USBtinyISP
programmers by their bus:device tuple.
* doc/avrdude.texi: Document the new functionality.
* avrdude.1: (Ditto.)
git-svn-id: svn://svn.savannah.nongnu.org/avrdude/trunk@974 81a1dc3b-b13d-400b-aceb-764788c761c2